A high-strength laminate made of small-diameter plantation wood: Flatwise bending mechanical properties

Abstract

The aim of this study was to explore the feasibility of manufacturing high-strength laminates from small-diameter plantation wood. A Chinese fir (Cunninghamia lanceolata) plantation comprising trees with a diameter at breast height of less than 30 cm was selected as the material in this study. The flatwise bending mechanical properties of the Chinese fir laminates with both non-finger-jointed (NFJ) and finger-jointed (FJ) were investigated. The results indicated that finger jointing did not affect the bending elastic modulus (MOE) of the laminates, but it could reduce the bending strength index and the coefficient of variation of the bending strength (MOR). Notably, an optimal correlation existed between the MOE and MOR for both NFJ and FJ laminates, indicating that the MOE could serve as the dominant control variable for the machine grading of laminates. The failure mode significantly influenced the bending mechanical properties of both the NFJ and FJ laminates, whose dominant failure modes were fiber failure near the knot and whole fractures of the finger jointing teeth roots, respectively. For both the NFJ and FJ laminates, the overall macroscopic morphology of the high-strength specimen was relatively flat, but the microscopic morphology was uneven owing to fiber pull out, while the low-strength specimen was the opposite. Compared to the traditional visual grading method, the proposed machine grading method could more scientifically and effectively identify the quality, reduce the coefficient of variation of the bending mechanical properties, and significantly improve the strength index of laminates. This study provides basic support for manufacturing high-strength laminates from small-diameter plantation wood.